A bicycle may be equipped with a component such as an adjustable seating assembly. Such a component may be advantageous to allow selective lowering and raising of a saddle while the bicycle is in operation. For example, a rider may benefit from a lower saddle height while descending an incline through greater control achieved by more range of motion. Conversely, a rider may benefit from a higher saddle height while ascending an incline through a position allowing greater power transfer to a drivetrain of the bicycle. By allowing selective height adjustment of the saddle during operation, the bicycle may be configured to provide an appropriate seating position for varying conditions.
A typical bicycle seating assembly may have a seat post that is mechanically clamped to a seat tube of the bicycle. The clamp may be a fastener or lever that is released to allow an increase in an inside diameter of the seat tube in order to facilitate sliding the seat post up or down, thus adjusting the saddle height. Such a seating assembly does not facilitate user-friendly adjustment while the bicycle is in operation. An adjustable seating assembly for a bicycle may be designed for relatively quick adjustment of the saddle height within a defined range. Such systems may commonly be known as dropper seat posts, and may also use remote activation to improve the usability during operation. Such remote activation may be actuated by cable tension, hydraulic pressure, electronic signal, or other actuation methods. The remote activation may trigger movement within a linear movement mechanism. The linear movement mechanism may include a spring, such as a coil spring or a pneumatic spring; an electronic device, such as a servo or motor, or another type of linear actuator or component thereof. Such a linear movement mechanism may be designed to provide power for movement in both a raising direction and a lowering direction, as with a reversible electric motor, or the linear movement mechanism may provide bias in only one direction, such as with a spring. For example, a pneumatic spring may be provided to bias the seating assembly in the raising direction with enough force that the saddle height may be increased by actuation while the rider is not applying downward force to the saddle but with less force than a gravitational force acting on the rider's mass applied to the saddle such that the rider's weight may be used to decrease the saddle height. A locking mechanism may be provided to prevent actuation of the linear movement mechanism and thus provide a stable seating platform at a fixed saddle height.
A hydraulic locking mechanism of an adjustable seating assembly biased in the raising direction may provide positive support of the seating assembly in the raising direction when the system is static and not actuated. The hydraulic locking mechanism may provide more finely modulated adjustment of saddle height in contrast to systems that use ratchet- or detent-type locking mechanisms. The hydraulic locking mechanism also avoids problems associated with friction-type locking mechanisms such as slippage. A hydraulic locking mechanism may function by supporting a movable portion of the seating assembly with an adjustable volume of minimally-compressible or non-compressible fluid, which may be referred to as non-compressible fluid for convenience. In general, non-compressibility will hereinafter refer to fluids, states, or components configured for insubstantial compressibility, such as in hydraulic fluids or pressure-transmitting configurations. For instance, a volume of hydraulic fluid may be contained within a support chamber of the seating assembly with a volume control valve selectively operable to allow adjustment of the volume. Conversely, the term compressible will refer to fluids with relatively high compressibility, such as those fluids in a gaseous state or which would substantially interfere with hydraulic pressure transfer.
The adjustable volume may be increased by a source of stored potential energy, such as a compressed pneumatic spring, being released to force part of a reservoir volume of hydraulic fluid into the support chamber, thus increasing the volume contained within the support chamber and increasing the saddle height. In this scenario, if the volume control valve is opened when the force of the rider's weight on the support chamber exceeds the force applied on the reservoir volume by the pneumatic spring, the volume of the support chamber and thus the saddle height will decrease. The force required to overcome the force of the spring bias may be tunable by adjusting pressure or working surface area of components.
Hydraulic systems relying on the non-compressibility of hydraulic fluid may degrade in performance due to ingress of compressible fluids. For example, gasses present in the atmosphere or contained within a pneumatic spring of the adjustable seating assembly may enter the hydraulic support chamber. Under pressure, these compressible fluids will compress and allow deflection of the adjustable seating assembly. In contrast, it may be advantageous to have no or very little movement in a seating assembly, for instance to promote more efficient energy transfer to the drivetrain of the bicycle. Because ingress of gasses may occur in a hydraulic system, a facility for releasing gasses from such a system may be advantageous. Such issues may also arise in other hydraulic components of a bicycle, for instance front and rear suspension components, to which such a facility may also apply.